Year: 2018
Type: dissertation
Abstract: Epithelial integrity defines the well-established positioning and communication of the epithelial cells within the tissue architecture, which is necessary for the epithelium to flawlessly perform its functions. Loss of tissue integrity is a hallmark of practically all advanced solid cancers. Tissue integrity can be lost by altered cell-cell, cell-matrix connections, and/or mislocalization of the proteins responsible for the establishment of cell polarity. It has been postulated that the abnormal proliferative behavior observed in cancer cells is not only a consequence but also requires loss of epithelial integrity. Early studies in Caenorhabditis elegans and Drosophila melanogaster have found evidence of the tumor suppression role of polarity regulating genes. In vertebrates, the role of polarity genes in cancer development is less clear, with only few polarity genes convincingly linked to tumorigenesis in animal cancer models. The general aim of the study was to clarify the role of epithelial integrity regulating genes in breast cancer development. The study primarily focused on cell cycle and epithelial architecture alterations induced by the shRNA-mediated silencing of putative epithelial integrity regulating genes. The targeted genes were selected based on available Drosophila genes knowledgebases. By exploiting the advantages of the three-dimensional (3D) cell cultures, which mimic the natural cell–cell and cell–extracellular matrix interactions, combined with genes knockdown and MYC oncogene activation, the study was able to identify novel putative tumor suppressor functions of genes regulating epithelial integrity. Specifically, the study unraveled a PARD6G tumor suppressor function linked to the modulation of the AKT signaling pathway, critical for cancer development. This study also exposed an unexpected synthetic lethality between loss of RHOA (small GTPase) and active MYC. The performed experiments indicate that the observed apoptosis is a consequence of an altered glutamine metabolism, important for the survival of cell with active MYC. Furthermore, a novel statistical framework was developed to efficiently analyze phenotypic data resulting from genetic screens performed in 3D cultures. Finally, the genetic profiling of patients’ derived breast cancer samples resulted in the identification of a genetic signature for tumors with disseminated tumor cells (DTC). Amongst this genetic signature, low RAI-2 expression was also correlated to patients’ poor prognosis. Further in vitro studies exposed a RAI-2 link to epithelial integrity regulation. In conclusion, this study successfully identified novel human epithelial integrity regulators in breast cancer, thereby opening potential therapeutic avenues for MYC-driven tumors and revealing a novel biomarker for early metastasis in breast cancer.
Source: Työväentutkimus Vuosikirja
Author: Elsa Marques
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
Funder: Helsingin Yliopisto
OpenAlex ID: W2895543140